1. Field of the Invention
The present invention relates to an optical apparatus, such as a camera including a digital camera, a video camera and a television camera which are used for a number of purposes, and particularly relates to a detector for detecting a position of a zoom lens with which the optical apparatus is provided.
2. Description of the Related Arts
In a camera in which a zoom lens is driven by a motor, it is necessary to perform a resetting operation for detecting a state of the zoom lens, for example when a position of a lens barrel forwarded from a body of the camera becomes unclear due to a loading and unloading of a battery into the camera.
For example, at time of performing the resetting operation, the detection is performed so that the zoom lens is driven until it mechanically contacts a barrel collapse end or a telephoto side end, and so that the mechanical contacting state is detected by a change, for example, of amount of rotation of the motor.
However, this resetting method for detecting the state of the zoom lens is not preferable because a greater load is exerted on the lens barrel and/or the zoom driving system.
On the other hand, another resetting method for detecting the state of the zoom lens is a method based upon a device in which there is mounted a switch that is able to detect the exact position of the zoom lens. According to the method, at time of performing the resetting operation, the position or the state, of the zoom lens, is detected by the switch.
However, this method requires a special switch and an additional space for accommodating the special switch inside a camera body, which causes the camera body to be larger necessarily and therefore causes its manufacturing cost to be higher.
On the other hand, in order to realize a miniaturization of the zoom lens and to realize a reduction of its manufacturing cost thereof, conventionally, there has been provided a zoom lens with a cam for moving a plurality of lenses thereof in which a plurality of focusing regions and zooming regions are arranged alternately to perform its zooming operation stepwise. According to this construction, it is possible to accomplish the zooming and focusing operations alternately without a particular focusing mechanism.
In this type of zoom lens, a detector (or a switch) to detect each reference position (or each standard position) of the lenses thereof for focusing at each zooming step, is required. In this construction, to provide a separate switch at each step is, however, disadvantageous, in view of a large space needed to accommodate such separate switches therein, and in view of a higher manufacturing cost necessarily incurred thereby. In this respect, therefore, it is advantageous to employ a single detector (or a switch) that is able to detect each position of the lenses of the zoom lens at each zooming step.
However, in case that such a single detector is employed therein, the same detection signal is outputted from the detector at a plurality of different zooming steps. Therefore, in this construction, it is not possible to specify each state, or each condition, of the zoom lens immediately at each step thereof.
Accordingly, in the construction, it is not easy to perform the resetting operation of the lenses of the zoom lens.